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The kinematic properties of BHB and RR Lyrae stars towards the Anticentre and the North Galactic Pole: the transition between the inner and the outer halo
We identify 51 blue horizontal branch (BHB) stars, 12 possible BHB starsand 58 RR Lyrae stars in Anticentre fields. Their selection does notdepend on their kinematics. Light curves and ephemerides are given forseven previously unknown RR Lyrae stars. All but four of the RR Lyraestars are of Oosterhoff type I.Our selection criteria for BHB stars give results that agree with thoseused by Smith et al. and Ruhland et al. We use five methods to determinedistances for the BHB stars and three methods for the RR Lyrae stars toget distances on a uniform scale. Absolute proper motions [largelyderived from the Second Guide Star Catalogue (GSCII) and Sloan DigitalSky Survey (Seventh Data Release) data bases] are given for these stars;radial velocities are given for 31 of the BHB stars and 37 of the RRLyrae stars.Combining these data for BHB and RR Lyrae stars with those previouslyfound in fields at the North Galactic Pole, we find that retrogradeorbits dominate for galactocentric distances greater than 12.5 kpc. Themajority of metal-poor stars in the solar neighbourhood are known to beconcentrated in a L? versus Lz angularmomentum plot. We show that the ratio of the number of outliers to thenumber in the main concentration increases with galactocentric distance.The location of these outliers with L? and Lzshows that the halo BHB and RR Lyrae stars have more retrograde orbitsand a more spherical distribution with increasing galactocentricdistance. Six RR Lyrae stars are identified in the H99 group ofoutliers; the small spread in their [Fe/H] suggests that they could havecome from a single globular cluster. Another group of outliers containstwo pairs of RR Lyrae stars; the stars in each pair have similarproperties.
| The Chemical Compositions of Variable Field Horizontal-branch Stars: RR Lyrae Stars
We present a detailed abundance study of 11 RR Lyrae ab-type variables:AS Vir, BS Aps, CD Vel, DT Hya, RV Oct, TY Gru, UV Oct, V1645 Sgr, WYAnt, XZ Aps, and Z Mic. High-resolution and high signal-to-noise ratioechelle spectra of these variables were obtained with the 2.5 m du Ponttelescope at the Las Campanas Observatory. We obtained more than 2300spectra, roughly 200 spectra per star, distributed more or lessuniformly throughout the pulsational cycles. A new method has beendeveloped to obtain the initial effective temperatures of our samplestars at a specific pulsational phase. We find that the abundance ratiosare generally consistent with those of similar metallicity field starsin different evolutionary states and throughout the pulsational cyclesfor RR Lyrae stars. TY Gru remains the only n-capture enriched staramong the RRab in our sample. A new relation is found betweenmicroturbulence and effective temperature among stars of thehorizontal-branch population. In addition, the variation ofmicroturbulence as a function of phase is empirically shown to besimilar to the theoretical variation. Finally, we conclude that thederived T eff and log g values of our sample stars follow thegeneral trend of a single mass evolutionary track.
| Radial Velocities and Pulsation Ephemerides of 11 Field RR Lyrae Stars
We present new radial velocities (RVs), improved pulsation periods, andreference epochs of 11 field RR Lyrae ab-type variables: AS Vir, BS Aps,CD Vel, DT Hya, RV Oct, TY Gru, UV Oct, V1645 Sgr, WY Ant, XZ Aps, and ZMic. This study is based on high-resolution spectra obtained with theechelle spectrograph of the 2.5 m du Pont telescope at Las CampanasObservatory. We obtained ~200 spectra per star (i.e., a total of ~2300spectra), distributed more or less uniformly throughout their pulsationcycles. RV curves and photometric light curves phased to our newephemerides are presented for all program stars. In a subsequent paper,we will use these spectra to derive stellar atmospheric parameters andchemical compositions throughout the pulsational cycles, based purely onspectroscopic constraints.
| RR Lyrae Atmospherics: Wrinkles Old and New. A Preview
I report some results of an echelle spectroscopic survey of RR Lyraestars begun in 2006 that I presented in my Henry Norris Lecture of 2010January 4. Topics include (1) atmospheric velocity gradients, (2)phase-dependent envelope turbulence as it relates to Peterson'sdiscoveries of axial rotation on the horizontal branch and to Stothers'explanation of the Blazhko effect, (3) the three apparitions of hydrogenemission during a pulsation cycle, (4) the occurrence of He I lines inemission and absorption, (5) detection of He II emission and metallicline doubling in Blazhko stars, and finally (6) speculation about whathelium observations of RR Lyrae stars in omega Centauri might tell usabout the putative helium populations and the horizontal branch of thatstrange globular cluster.This paper preserves the substance and style of remarks that accompaniedthe author's PowerPoint presentation of the 2009 Henry Norris Russelllecture.
| Helium lines in RR Lyrae spectra
Context: During a comparative study of atmospheric phenomena that occurduring the pulsation cycles of 10 RRab stars I unexpectedly found heliumlines in emission and/or absorption in all 10 stars during rising light.The progression of events in the time-evolution of the helium spectrumdiffers in detail from star to star, but 9 of the 10 stars share anumber of general characteristics, illustrated approximately by thebehavior of RV Oct described in this Note. Aims: Mylong-term aim is to provide a comprehensive empirical description ofatmospheric phenomena that take place during the pulsation cycles ofRRab stars. The short-term goal of this paper is to inform readers thatmeasurements of helium lines place new constraints on shock-wave modelsfor RRab stars. Methods: Results presented here are based onmeasurements and analysis of observations made with the echellespectrograph of the du Pont 2.5-m telescope at Las CampanasObservatory. Results: A general pattern of behavior emergesalbeit with significant star-to-star variation. He I ? 5376 (D3)appears first as a pure emission feature, unlike the Balmer lines forwhich the emission profile is always overlain initially by strongredward-displaced absorption. The phase of maximum D3 emission coincidesapproximately with that of H?, but the duration of conspicuous D3emission (in excess of the local continuum) is less than 15 mn,approximately half the duration of similarly defined H? emission.The emission phase is followed by the appearance, first, ofredward-displaced absorption, and shortly thereafter by a secondviolet-displaced absorption component that strengthens with advancingphase. Both absorption components gradually weaken and disappear afterradial-velocity minimum, which lags luminosity maximum by no more than0.01P as discussed in Sect. 3. However, bona fide He I ? 5876emission flux in excess of the local continuum flux reappears nearmaximum light for some stars in the sample and persists for about 45 mn.The radial velocities of the initial and final He I ? 5876emission features differ little from the time-average value of themetallic-line radial velocities for RV Octantis. However, the absorptionfeatures appear to distort the location of the emission centroid, whenthey are strong.
| The luminosities and distance scales of type II Cepheid and RR Lyrae variables
Infrared and optical absolute magnitudes are derived for the type IICepheids κ Pav and VY Pyx using revised Hipparcos parallaxes andfor κ Pav, V553 Cen and SW Tau from pulsational parallaxes.Revised Hipparcos and HST parallaxes for RR Lyrae agree satisfactorilyand are combined in deriving absolute magnitudes. Phase-corrected J, Hand Ks mags are given for 142 Hipparcos RR Lyraes based onTwo-Micron All-Sky Survey observations. Pulsation and trigonometricalparallaxes for classical Cepheids are compared to establish the bestvalue for the projection factor (p) used in pulsational analyses.The MV of RR Lyrae itself is 0.16 +/- 0.12 mag brighter thanpredicted from an MV-[Fe/H] relation based on RR Lyrae starsin the Large Magellanic Cloud (LMC) at a modulus of 18.39 +/- 0.05 asfound from classical Cepheids. This is consistent with the prediction ofCatelan & Cortés that it is overluminous for its metallicity.The results for the metal- and carbon-rich Galactic disc stars, V553 Cenand SW Tau, each with small internal errors (+/-0.08 mag) have a meandeviation of only 0.02 mag from the period-luminosity (PL) relationestablished by Matsunaga et al. for type II Cepheids in globularclusters and with a zero-point based on the same LMC-scale. Comparingdirectly the luminosities of these two stars with published data on typeII Cepheids in the LMC and in the Galactic bulge leads to an LMC modulusof 18.37 +/- 0.09 and a distance to the Galactic Centre of R0= 7.64 +/- 0.21kpc. The data for VY Pyx agree with these results withinthe uncertainties set by its parallax. Evidence is presented thatκ Pav may have a close companion and possible implications of thisare discussed. If the pulsational parallax of this star is incorporatedin the analyses, the distance scales just discussed will be increased by~0.15 +/- 0.15 mag. V553 Cen and SW Tau show that at optical wavelengthsPL relations are wider for field stars than for those in globularclusters. This is probably due to a narrower range of masses in thelatter case.
| The GEOS RR Lyr Survey
Not Available
| Proper identification of RR Lyrae stars brighter than 12.5 mag
RR Lyrae stars are of great importance for investigations of Galacticstructure. However, a complete compendium of all RR-Lyraes in the solarneighbourhood with accurate classifications and coordinates does notexist to this day. Here we present a catalogue of 561 local RR-Lyraestars (V_max ≤ 12.5 mag) according to the magnitudes given in theCombined General Catalogue of Variable Stars (GCVS) and 16 fainter ones.The Tycho2 catalogue contains ≃100 RR Lyr stars. However, manyobjects have inaccurate coordinates in the GCVS, the primary source ofvariable star information, so that a reliable cross-identification isdifficult. We identified RR Lyrae from both catalogues based on anintensive literature search. In dubious cases we carried out photometryof fields to identify the variable. Mennessier & Colome (2002,A&A, 390, 173) have published a paper with Tyc2-GCVSidentifications, but we found that many of their identifications arewrong.
| RR Lyrae stars: kinematics, orbits and z-distribution
RR Lyrae stars in the Milky Way are good tracers to study the kinematicbehaviour and spatial distribution of older stellar populations. Arecently established well documented sample of 217 RR Lyr stars withV<12.5 mag, for which accurate distances and radial velocities aswell as proper motions from the Hipparcos and Tycho-2 catalogues areavailable, has been used to reinvestigate these structural parameters.The kinematic parameters allowed to calculate the orbits of the stars.Nearly 1/3 of the stars of our sample have orbits staying near the MilkyWay plane. Of the 217 stars, 163 have halo-like orbits fulfilling one ofthe following criteria: Θ < 100 km s-1, orbiteccentricity >0.4, and normalized maximum orbital z-distance>0.45. Of these stars roughly half have retrograde orbits. Thez-distance probability distribution of this sample shows scale heightsof 1.3±0.1 kpc for the disk component and 4.6±0.3 kpc forthe halo component. With our orbit statistics method we found a(vertical) spatial distribution which, out to z=20 kpc, is similar tothat found with other methods. This distribution is also compatible withthe ones found for blue (HBA and sdB) halo stars. The circular velocityΘ, the orbit eccentricity, orbit z-extent and [Fe/H] are employedto look for possible correlations. If any, it is that the metal poorstars with [Fe/H] <1.0 have a wide symmetric distribution aboutΘ=0, thus for this subsample on average a motion independent ofdisk rotation. We conclude that the Milky Way possesses a halo componentof old and metal poor stars with a scale height of 4-5 kpc having randomorbits. The presence in our sample of a few metal poor stars (thus partof the halo population) with thin disk-like orbits is statistically notsurprising. The midplane density ratio of halo to disk stars is found tobe 0.16, a value very dependent on proper sample statistics.
| Subsystems of RR Lyrae Variable Stars in Our Galaxy
We have used published, high-accuracy, ground-based and satelliteproper-motion measurements, a compilation of radial velocities, andphotometric distances to compute the spatial velocities and Galacticorbital elements for 174 RR Lyrae (ab) variable stars in the solarneighborhood. The computed orbital elements and published heavy-elementabundances are used to study relationships between the chemical,spatial, and kinematic characteristics of nearby RR Lyrae variables. Weobserve abrupt changes of the spatial and kinematic characteristics atthe metallicity [Fe/H]≈-0.95 and also when the residual spatialvelocities relative to the LSR cross the critical value V res≈290km/s. This provides evidence that the general population of RR Lyraestars is not uniform and includes at least three subsystems occupyingdifferent volumes in the Galaxy. Based on the agreement between typicalparameters for corresponding subsystems of RR Lyrae stars and globularclusters, we conclude that metal-rich stars and globular clusters belongto a rapidly rotating and fairly flat, thick-disk subsystem with a largenegative vertical metallicity gradient. Objects with larger metaldeficiencies can, in turn, be subdivided into two populations, but usingdifferent criteria for stars and clusters. We suggest that field starswith velocities below the critical value and clusters with extremelyblue horizontal branches form a spherical, slowly rotating subsystem ofthe protodisk halo, which has a common origin with the thick disk; thissubsystem has small but nonzero radial and vertical metallicitygradients. The dimensions of this subsystem, estimated from theapogalactic radii of orbits of field stars, are approximately the same.Field stars displaying more rapid motion and clusters with redderhorizontal branches constitute the spheroidal subsystem of the accretedouter halo, which is approximately a factor of three larger in size thanthe first two subsystems. It has no metallicity gradients; most of itsstars have eccentric orbits, many display retrograde motion in theGalaxy, and their ages are comparatively low, supporting the hypothesisthat the objects in this subsystem had an extragalactic origin.
| Bias Properties of Extragalactic Distance Indicators. XI. Methods to Correct for Observational Selection Bias for RR Lyrae Absolute Magnitudes from Trigonometric Parallaxes Expected from the Full-Sky Astrometric Mapping Explorer Satellite
A short history is given of the development of the correction forobservation selection bias inherent in the calibration of absolutemagnitudes using trigonometric parallaxes. The developments have beendue to Eddington, Jeffreys, Trumpler & Weaver, Wallerstein,Ljunggren & Oja, West, Lutz & Kelker, after whom the bias isnamed, Turon Lacarrieu & Crézé, Hanson, Smith, andmany others. As a tutorial to gain an intuitive understanding of severalcomplicated trigonometric bias problems, we study a toy bias model of aparallax catalog that incorporates assumed parallax measuring errors ofvarious severities. The two effects of bias errors on the derivedabsolute magnitudes are (1) the Lutz-Kelker correction itself, whichdepends on the relative parallax error δπ/π and the spatialdistribution, and (2) a Malmquist-like ``incompleteness'' correction ofopposite sign due to various apparent magnitude cutoffs as they areprogressively imposed on the catalog. We calculate the bias propertiesusing simulations involving 3×106 stars of fixedabsolute magnitude using Mv=+0.6 to imitate RR Lyraevariables in the mean. These stars are spread over a spherical volumebounded by a radius 50,000 pc with different spatial densitydistributions. The bias is demonstrated by first using a fixed rmsparallax uncertainty per star of 50 μas and then using a variable rmsaccuracy that ranges from 50 μas at apparent magnitude V=9 to 500μas at V=15 according to the specifications for the Full-SkyAstrometric Mapping Explorer (FAME) satellite to be launched in 2004.The effects of imposing magnitude limits and limits on the``observer's'' error, δπ/π, are displayed. We contrast themethod of calculating mean absolute magnitude directly from theparallaxes where bias corrections are mandatory, with an inverse methodusing maximum likelihood that is free of the Lutz-Kelker bias, althougha Malmquist bias is present. Simulations show the power of the inversemethod. Nevertheless, we recommend reduction of the data using bothmethods. Each must give the same answer if each is freed from systematicerror. Although the maximum likelihood method will, in theory, eliminatemany of the bias problems of the direct method, nevertheless the biascorrections required by the direct method can be determined empiricallyvia Spaenhauer diagrams immediately from the data, as discussed in theearlier papers of this series. Any correlation of the absolute(trigonometric) magnitudes with the (trigonometric) distances is thebias. We discuss the level of accuracy that can be expected in acalibration of RR Lyrae absolute magnitudes from the FAME data over themetallicity range of [Fe/H] from 0 to -2, given the known frequency ofthe local RR Lyrae stars closer than 1.5 kpc. Of course, use will alsobe made of the entire FAME database for the RR Lyrae stars over thecomplete range of distances that can be used to empirically determinethe random and systematic errors from the FAME parallax catalog, usingcorrelations of derived absolute magnitude with distance and position inthe sky. These bias corrections are expected to be much more complicatedthan only a function of apparent magnitude because of variousrestrictions due to orbital constraints on the spacecraft.
| Absolute Magnitudes and Kinematic Parameters of the Subsystem of RR Lyrae Variables
The statistical parallax technique is applied to a sample of 262 RRabLyrae variables with published photoelectric photometry, metallicities,and radial velocities and with measured absolute proper motions.Hipparcos, PPM, NPM, and the Four-Million Star Catalog (Volchkov et al.1992) were used as the sources of proper motions; the proper motionsfrom the last three catalogs were reduced to the Hipparcos system. Wedetermine parameters of the velocity distribution for halo [(U_0, V_0,W_0) = (-9 +/- 12, -214 +/- 10, -16 +/- 7) km/s and (sigma_U, sigma_V,sigma_W) = (164 +/- 11, 105 +/- 7, 95 +/- 7) km/s] and thick-disk [(U_0,V_0, W_0) = (-16 +/- 8, -41 +/- 7, -18 +/- 5) km/s and (sigma_U,sigma_V, sigma_W) = (53 +/- 9, 42 +/- 8, 26 +/- 5) km/s] RR Lyrae, aswell as the intensity-averaged absolute magnitude for RR Lyrae of thesepopulations: = 0.77 +/- 0.10 and = +1.11 +/-0.28 for the halo and thick-disk objects, respectively. The metallicitydependence of the absolute magnitude of RR Lyrae is analyzed(=(0.76 +/- 0.12) + (0.26 +/- 0.26) x ([Fe/H] + 1.6) = 1.17 +0.26 x [Fe/H]). Our results are in satisfactory agreement with the_(RR)-[Fe/H] relation from Carney et al. (1992)(_(RR) = 1.01 + 0.15 x [Fe/H]) obtained by Baade-Wesselink'smethod. They provide evidence for a short distance scale: the LMCdistance modulus and the distance to the Galactic center are 18.22 +/-0.11 and 7.4 +/-±0.5 kpc, respectively. The zero point ofthe distance scale and the kinematic parameters of the RR Lyraepopulations are shown to be virtually independent of the source ofabsolute proper motions used and of whether they are reduced to theHipparcos system or not.
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| Kinematics of Metal-poor Stars in the Galaxy. II. Proper Motions for a Large Nonkinematically Selected Sample
We present a revised catalog of 2106 Galactic stars, selected withoutkinematic bias and with available radial velocities, distance estimates,and metal abundances in the range -4.0<=[Fe/H]<=0.0. This updateof the 1995 Beers & Sommer-Larsen catalog includes newly derivedhomogeneous photometric distance estimates, revised radial velocitiesfor a number of stars with recently obtained high-resolution spectra,and refined metallicities for stars originally identified in the HKobjective-prism survey (which account for nearly half of the catalog)based on a recent recalibration. A subset of 1258 stars in this cataloghave available proper motions based on measurements obtained with theHipparcos astrometry satellite or taken from the updated AstrographicCatalogue (second epoch positions from either the Hubble Space TelescopeGuide Star Catalog or the Tycho Catalogue), the Yale/San Juan SouthernProper Motion Catalog 2.0, and the Lick Northern Proper Motion Catalog.Our present catalog includes 388 RR Lyrae variables (182 of which arenewly added), 38 variables of other types, and 1680 nonvariables, withdistances in the range 0.1 to 40 kpc.
| Systematics of RR Lyrae Statistical Parallax. III. Apparent Magnitudes and Extinctions
We sing the praises of the central limit theorem. Having previouslyremoved all other possible causes of significant systematic error in thestatistical-parallax determination of RR Lyrae absolute magnitudes, weinvestigate systematic errors from two final sources of input data:apparent magnitudes and extinctions. We find corrections due to each ofabout 0.05 mag, i.e., about half the statistical error. However, theseare of opposite sign and so approximately cancel out. Theapparent-magnitude system that we previously adopted from Layden et al.was calibrated to the photoelectric photometry of Clube & Dawe.Using Hipparcos photometry and archival modern ground-based photometry,we show that the Clube & Dawe system is about 0.06 mag too bright.Extinctions were previously based on the map of Burstein & Heiles,which was constructed from H I maps. We argue that extinctions shouldrather be estimated using the new map of Schlegel, Finkbeiner, &Davis based on COBE and IRAS measurements of dust emission. Thissubstitution increases the mean estimated extinction by about 0.05 mag,primarily because of a difference in the zero point of the two maps. Ourfinal estimate for the absolute magnitude is M_V = 0.77 +/- 0.13 at[Fe/H] = -1.60 for a pure sample of 147 halo RR Lyrae stars, or M_V =0.80 +/- 0.11 at [Fe/H] = -1.71 if we incorporate kinematic informationfrom 716 nonkinematically selected non-RR Lyrae stars from Beers &Sommer-Larsen. These are 2 and 3 sigma fainter than recentdeterminations of M_V based on main-sequence fitting of clusters usingHipparcos measurements of subdwarfs by Reid and Gratton et al. Sincestatistical parallax is being cleared of systematic errors and since theprobability of a more than 2 sigma statistical fluctuation is less than1/20, we conclude that these brighter determinations may be in error. Inthe course of these three papers, we have corrected six systematicerrors whose absolute values total 0.20 mag. Had these, contrary to theexpectation of the central limit theorem, all lined up one way, theycould have resolved the conflict in favor of the brighterdeterminations. In fact, the net change was only 0.06 mag.
| The absolute magnitudes of RR Lyraes from HIPPARCOS parallaxes and proper motions
We have used HIPPARCOS proper motions and the method of StatisticalParallax to estimate the absolute magnitude of RR Lyrae stars. Inaddition we used the HIPPARCOS parallax of RR Lyrae itself to determineit's absolute magnitude. These two results are in excellent agreementwith each other and give a zero-point for the RR Lyrae M_v,[Fe/H]relation of 0.77+/-0.15 at [Fe/H]=-1.53. This zero-point is in goodagreement with that obtained recently by several groups usingBaade-Wesselink methods which, averaged over the results from thedifferent groups, gives M_v = 0.73+/-0.14 at [Fe/H]=-1.53. Taking theHIPPARCOS based zero-point and a value of 0.18+/-0.03 for the slope ofthe M_v,[Fe/H] relation from the literature we find firstly, thedistance modulus of the LMC is 18.26+/-0.15 and secondly, the mean ageof the Globular Clusters is 17.4+/-3.0 GYrs. These values are comparedwith recent estimates based on other "standard candles" that have alsobeen calibrated with HIPPARCOS data. It is clear that, in addition toastrophysical problems, there are also problems in the application ofHIPPARCOS data that are not yet fully understood. Table 1, whichcontains the basic data for the RR Lyraes, is available only at CDS. Itmay be retrieved via anonymous FTP at cdsarc.u-strasbg.fr (130.79.128.5)or via the Web at http://cdsweb.u-strasbg.fr/Abstract.html
| Early evolution of the Galactic halo revealed from Hipparcos observations of metal-poor stars
The kinematics of 122 red giant and 124 RR Lyrae stars in the solarneighborhood are studied using accurate measurements of their propermotions obtained by the Hipparcos astrometry satellite, combined withtheir published photometric distances, metal abundances, and radialvelocities. A majority of these sample stars have metal abundances of(Fe/H) = -1 or less and thus represent the old stellar populations inthe Galaxy. The halo component, with (Fe/H) = -1.6 or less, ischaracterized by a lack of systemic rotation and a radially elongatedvelocity ellipsoid. About 16 percent of such metal-poor stars have loworbital eccentricities, and we see no evidence of a correlation between(Fe/H) and e. Based on the model for the e-distribution of orbits, weshow that this fraction of low-e stars for (Fe/H) = -1.6 or less isexplained by the halo component alone, without introducing the extradisk component claimed by recent workers. This is also supported by theabsence of a significant change in the e-distribution with height fromthe Galactic plane. In the intermediate-metallicity range, we find thatstars with disklike kinematics have only modest effects on thedistributions of rotational velocities and e for the sample at absolutevalue of z less than 1 kpc. This disk component appears to constituteonly 10 percent for (Fe/H) between -1.6 and -1 and 20 percent for (Fe/H)between -1.4 and -1.
| Kinematics of metal-poor stars in the galaxy
We discuss the kinematic properties of a sample of 1936 Galactic stars,selected without kinematic bias, and with abundances (Fe/H) is less thanor equal to -0.6. The stars selected for this study all have measuredradial velocities, and the majority have abundances determined fromspectroscopic or narrow-/intermediate-band photometric techniques. Incontrast to previous examinations of the kinematics of the metal-poorstars in the Galaxy, our sample contains large numbers of stars that arelocated at distances in excess of 1 kpc from the Galactic plane. Thus, amuch clearer picture of the nature of the metal-deficient populations inthe Galaxy can now be drawn.
| The metallicities and kinematics of RR Lyrae variables, 1: New observations of local stars
In order to study the structure and formation history of the galaxy, wehave obtained low-to-moderate dispersion spectra of 302 nearby RR Lyraevariables of Bailey type 'ab'. We derived abundances, typically accurateto 0.15-0.20 dex and calibrated to the Zinn & West (1984) globularcluster metallicity scale, from the pseudoequivalent widths of the Ca IIK, H delta, H gamma, and H beta lines. Radial velocities accurate tobetween 2 and 30 km/s were obtained from the spectra and from theliterature. Distances accurate to between 5% and 20% were derived frompublished apparent magnitudes and Burstein & Heiles (1982)reddenings. The metallicity distribution of the RR Lyrae stars peaks at(Fe/H)K approximately equals -1.5, and is narrower than thatof the Ryan & Norris (1991) subdwarfs, as expected since the mostmetal-rich and metal-poor progenitors preferentially appear as stablered and blue horizontal branch stars, rather than as RR Lyrae. Themetal-rich tail of the RR Lyrae distribution extends to(Fe/H)K approximately equals 0, and a qualitative analysis ofthe distribution of distances from the galactic plane shows that thestars in this tail (i.e., (Fe/H)K greater than -1.0) are moreconcentrated to the plane than the more metal-poor stars. The abundancedistribution of the local RR Lyrae stars is in excellent agreement withthe changing abundance distributions of distant RR Lyrae stars as afunction of galactocentric distance, as derived by Suntzeff et al.(1991), who ascribed this change to systematic variation in horizontalbranch morphology (probably age variations) with galactocentricdistance. The abundance distribution of the local RR Lyrae stars alsoagrees well with those of the distant RR Lyrae stars as a function ofdistance from the galactic plane. There is no evidence for an abundancegradient in this direction, suggesting that gaseous dissipation did notplay a major role in the formation of the outer halo.
| The Oosterhoff period effect - Luminosities of globular cluster zero-age horizontal branches and field RR Lyrae stars as a function of metallicity
Abstract image available at:http://adsabs.harvard.edu/abs/1990ApJ...350..631S
| Population studies. II - Kinematics as a function of abundance and galactocentric position for (Fe/H) of -0.6 or less
A catalog is presented of some 1200 Galactic objects which have radialvelocities and (Fe/H) abundances of -0.6 or less. These data areanalyzed to yield information on the kinematic properties of the olderpopulations of the Galaxy and on the interdependence between kinematicsand abundance. It is found that the kinematics of the availablekinematically selected stars differ from those of the nonkinematicallyselected objects. No evidence is found for any significant difference inthe kinematic properties of the various halo subgroups, nor for anydependence of kinematics on abundance. While the rotation of the halo issmall at about 37 km/s for (Fe/H) of -1.2 or less, it rises quickly forhigher abundances to a value of about 160 km/s at (Fe/H) = 0.6. Objectsin the abundance range -0.9 to -0.6 appear to belong predominantly to apopulation possessing the kinematic characteristics of a thick disk. Theimplications of these findings for the suggestion that globular clustersbelong to the same population as the noncluster objects, for the originof the thick disk, and for the mass of the Galaxy are discussed.
| Supergiant OH/IR stars
OH was detected toward six stars out of approximately 70 M supergiantsthat were searched for type I OH emissions, but is in most cases thoughtto not be associated with these stars. It is indicated by the results ofthis survey, in combination with earlier searches for Type II OHsupergiants, that OH luminosities are lower for Type I than Type IIsupergiants. Effects similar to a trend toward OH luminosity increaseswith IR color index have been noted for OH Miras, though these starsgenerally have smaller OH luminosities and color indexes. Results arefound to be consistent with OH supergiants having thicker dust envelopesthan most OH Miras.
| Reddening and blanketing of RR Lyrae stars
Based on complete light curves in the five channels of the WalravenVBLUW photometric system, a discussion is given of the determination ofblanketing and reddening for RR Lyrae stars. A photometric accuracy ofthe order of 0.005 mag has been reached. Blanketing derived from thereddening-free color index /B-L/ is shown to be equivalent to other waysof determining the metallicity of RR Lyrae stars, such as delta (u-B)s,m1, and delta S. Two independent ways to find the interstellar-reddeningcorrection are studied; they lead to identical results. A table is givenwith high-accuracy blanketing and reddening values for 73 RRab, 13 RRc,and a few short-period (RRs) variables. The relation between the presentobservations and those in other intermediate-band systems is considered.
| An atlas of light and colour curves of field RR Lyrae stars
An atlas is presented of light and color curves in the Walraven VBLUWphotometric system for 90 field RR Lyrae and short-period variables. Theobservational program and the reduction procedure are briefly described.Tables are presented containing the colors at mean and minimum light.
| Absolute magnitudes and motions of RR Lyrae stars
Absolute magnitudes are found by the use of statistical parallax for RRLyrae stars which have been grouped by period and by metal type. TheBailey c-type stars are treated independently. Solar motion solutionsare made using velocity data. Parameters of galactic orbits obtainedfrom space velocities show a relation to period. For the total a-stargroup the resultant mean light visual absolute magnitude is 0.49 mag,which corresponds to MB of 0.63 mag. Using this figure, thedistance to the galactic center is 9.3 kpc.
| Intermediate Band Photometry of BB Lyrae Stars. II. Colors of RR Lyrae and Ultra-Short Period Variables
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973ApJS...25..487J&db_key=AST
| Observations of southern RR Lyrae stars
Not Available
| Discussion of photo-electric five-colour observations of different types of pulsating variables
Not Available
| Spectral Classifications for 112 Variable Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1960ApJ...131..632H&db_key=AST
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| Takýmyýldýz: | Mikroskop |
| Sað Açýklýk: | 21h16m22.70s |
| Yükselim: | -30°17'03.0" |
| Görünürdeki Parlaklýk: | 11.512 |
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